1) Field of the Invention
The present invention relates to a positive-tone photosensitive polymer composition, which is converted into a heat resistant polymer after curing, and applied to a passivation film, interlayer insulating film and the like for semiconductor devices in electronic equipments.
2) Description of the Related Art
Since polyimides have excellent heat resistance, good mechanical properties, they can be formed in films easily, their surface is relatively flat, and the like, the polyimides are widely used as passivation films or interlayer insulating films in semiconductor devices. In the semiconductor devices in which the polyimides are used as the passivation films or the interlayer insulating films, through-holes can be formed in the semiconductor devices by etching the semiconductor devices with a positive-tone photoresist. However, such etching is complicated because it involves applying the photoresist and peeling off the photoresist. Photosensitive heat resistant materials have been investigated as a means to obtain a better method of forming the through-holes.
The photosensitive heat resistant composition, which is usually in the form of a liquid, is applied onto the semiconductor substrate, dried, irradiated with active ray via a mask, and un-exposed area of the substrate is removed by a developer. This results in a formation of a pattern of the semiconductor substrate. The photosensitive heat resistant materials include, for example, following two compositions:                1) polyimide precursor composition in which a photosensitive group is introduced by ester bonding (see Japanese Patent Application Publication No. 55-30207), and        2) composition prepared by adding a compound containing a carbon-carbon double bond dimeriazable or polymerizable by chemical ray to a polyamic acid, an amino group, and an aromatic bisazide (see Japanese Patent Application Publication No. 3-36861.        
However, both the above-mentioned compositions have negative-tone, and an organic solvent is used in the development process during pattern formation. Therefore, there is a problem that the arrangement that performs the masking and development is need to be changed when switching from an etching process using a positive-tone photoresist to a negative-tone photosensitive heat resistant material and vice versa.
Therefore, positive-tone photosensitive heat resistant compositions developable with an alkali aqueous solution has been investigated. Following two positive-tone photosensitive heat resistant compositions, for example, have been reported:                1) composition containing a polyamic acid ester containing a phenolic hydroxyl group and an o-quinonediazide compound (see Japanese Patent Application Laid-Open No. 4-204945), and        2) composition containing a polybenzoxazole precursor and an o-quinonediazide compound (Japanese Patent Application Laid-Open No. 1-46862).        
Thus, both of the above-mentioned compositions include the o-quinonediazide compound as a photosensitive agent. However, the o-quinonediazide compound has a problem that it absorbs the exposure wavelengths. Therefore, there is a problem with the above-mentioned two positive-tone photosensitive heat resistant compositions that their sensitivity is low when they are formed in thick films.
There is a report (see Japanese Patent No. 3015430) on a composition containing a polymer prepared by protecting carboxyl groups of a polyamic acid and a compound generating an acid by irradiation. This composition is theoretically supposed to be high sensitivity because acids generated by irradiation can de-protect a protected carboxyl group several times. However, in reality the sensitivity is low, and it is not practical to employ this composition.
Some of the semiconductor device structures require that the temperature be low during the heat-treatment for converting a polyimide precursor into a polyimide. However, conventional materials have a problem that if the temperature during the heat-treatment is low, the polyimide does not spread effectively.